Loading rate effect on fracture process in Brazilian splitting tests of Beishan granites

Abstract

In the present study, to reveal the loading rate effect on fracture process in Beishan granite, a series of Brazilian splitting tests under conventionally monotonic loading and stepwise loading conditions were performed to observe the crack propagation process of granites, with the aid of a digital image correlation (DIC) technique. The fracture process zone (FPZ) length and opening displacement ahead of notch tips, and so on were measured, and the loading-rate dependence was acquired correspondingly. The experimental results show that the peak load, axial and lateral deformation of granite gradually increased with the increasing loading rate. With the increase in the loading rate, the stress level for fracture initiation decreased, while the critical opening displacement and FPZ length gradually increased. The granite underwent insignificant deformation during the constant stress loading period when a lower stress was applied. When a larger stress was applied, obvious three-stage creep deformation was observed. The opening displacement ahead of notch tips increased slowly at a constant rate during the primary and secondary creep stages, then exhibited an approximately exponential increase with increasing time during the tertiary creep. Moreover, the FPZ length of granite at the critical state under conventional loading was higher than that under stepwise loading. The inner mechanism is analyzed to explain the rate-dependent fracturing behavior.